THE PLANET VENUS.

165

These effects may be in some way connected with the natureof its cloudy, or vaporous envelopes, but we cannot say thatany thoroughly satisfactory explanation of them has as yetbeen given. It has sometimes been stated that the outer edgeof the crescent phase appears to be its brightest part; butcareful observations, in which its light has been continuouslydiminished by the use of a wedge of dark glass, have indicatedthat the brightest part is not at the outer edge, but somewhatwithin it, so that the light is reflected, to some extent, as itwould be from a vitrified or polished spherical surface, inwhich one special spot would shine with surpassing brilliancy.Hence it has been recently suggested that the reflection of thelight of Venus may be specular, or mirror-like; an idea whichmust, however, be considered to be extremely hypothetical. Itmay, moreover, be well that any such hypothesis should beallowed to lie by for the present, as its suggestion originateda considerable amount of rather animated controversy.

Much more certain are the indications of an atmosphereof the planet, which are afforded by the extension of thecusps, or fine terminating points of the crescent, beyond asemi-circumference, into the darkened part of the disc. Thishas been noticed by Sir W. Herschel, as well as by Schroter,and by many others in more recent times. Observations havealso been made by Professor Lyman, of Yale College , U.S.,and, we believe, by at least one other observer, of a fine threadof light seen all round the planet, at the time of its inferiorconjunction, when its dark side is altogether turned towardsthe Earth . And certainly during its transits in 1761, 1769,and again in 1874, both just before and after it entered uponthe Sun’s disc, a ring of light indicating an atmosphere ofconsiderable refractive power was seen.

AYe have therefore very good grounds for believing that Venus is possessed of an atmosphere ; which we also suppose to beheavily laden with clouds, owing to the brilliancy of the lightreflected to our gaze.

AYe have already discussed the transits of Venus in our firstlecture upon the Sun, in which we explained their exceptionalimportance in reference to the determination of the Sun’s